Evidence of Common Descent The Fossil Record Remains

Evidence of Common Descent

The Fossil Record • Remains of organisms=fossils • Present in sedimentary rock • Formed by – Preservation of whole organism: amber, ice, tar – Preservation of hard parts: shells, bones, teeth – Petrified; mineral replacement – Sedimentation: buried, leaving imprint, mold, cast

Distribution of Fossils • Law of Superposition: layers of rock or soil are deposited on top of one another by water or wind. • Oldest layers are near the bottom; youngest are at the top, fossils found in the same layer are about the same age • Can see changes in climate over time

Homologous Structures: Comparative Anatomy • Body parts with same origin and structure but different function – Demonstrates common ancestry and genetic relationships • Ex. Beaks of birds • Ex. Forelimbs of penguin, alligator, bat and human – Why different in function? Different survival needs

Analogous Structures • Similar structures with identical functions that have no anatomical or embryological significance – Ex. Bird wind and insect wing – Ex. Vestigial organs • Organs useful in an ancestor, but useless in a modern species • In humans—coccyx; appendix

Similarities in Embryos • Comparative Embryology – Sign of common ancestry

Similarities in Chemical Makeup • Comparative Biochemistry – All have DNA/RNA similar organic compounds, organelles – Closer the relationship, closer the protein structure – Ex. Similarity between hemoglobin molecules in various organisms

2. 2 Recap 1. How do scientists know evolution happened? fossils 2. The oldest sediments are found at which layer of soil? bottom 3. What do fossil records reveal? changes in organisms; change in climate 4. What are homologous structures? same basic structure, different functions 5. Similarities in the chemical makeup is called comparative biochemistry

Patterns of Evolution • Coevolution – Change of two or more species in close association with each other • Ex. Plants and pollinators • Convergent evolution – Organisms in same environment adapt in a similar manner to that environment • Ex. Shark and porpoise

• Divergent evolution – Two related species become more and more different in response to differing habitats • Adaptive radiation – Evolution of marsupials of Australia from a common ancestor; Galapagos finches • Artificial selection – Selectively breeding dogs

Phylogenetic Trees • A phylogenetic tree, represents the evolutionary relationships among a set of organisms or groups of organisms, called taxa. • The tips of the tree represent species. • The nodes on the tree represent the common ancestors of those descendants. • Two descendants that split from the same node are called sister groups. In the tree below, species A & B are sister groups — they are each other's closest relatives. • Many phylogenies also include an outgroup — a taxon outside the group of interest. All the members of the group of interest are more closely related to each other than they are to the outgroup.

Cladistics • Cladistics gets its name from the branches on the family tree, which are called clades. A cladogram is a stylized diagram that looks like a series of Y's or forks in a road. At each branch, or "Y" junction, novel characters of evolutionary origin are used to separate off one group from the rest. • Ancestral characteristic: shared with the organisms lower on the cladogram • Derived characteristic: new trait not shared with organisms lower on the cladogram

In 1961, Patricia Jevons, an English bacteriologist, discovers a methicillin-resistant strain of Staphylococcus aureus (MRSA) in English hospitals. British scientist Alexander Fleming discovers and isolates penicillin, the first-known antibiotic substance. 50% of hospital Staphylococcus aureus infections in the US are identified as MRSA. Penicillin is used in England the US to fight Staphylococcus aureus infections. 2% of hospital Staphylococcus aureus infections in the US are identified as methicillin resistant (MRSA). Hospitals report that 25% of Staphylococcus aureus infections are penicillin resistant. The antibiotic methicillin, among others, is introduced to fight penicillin resistant Staphylococcus aureus infections. In the late 1880 s, Alexander Ogston, a Scottish surgeon, identifies the bacterium Today, over 95% of Staphylococcus aureus is penicillin resistant and 60% is methicillin resistant